What is the meaning of Model(s, a) in the prioritized sweeping algorithm?
I think pseudocode was made for tabular case with an assumption of deterministic environment. $Model(s, a)$ would then be a table with information of the next state and reward after taking action $a$ from state $s$. The size of that table would be same as the size of Q table. Because the environment is deterministic you wouldn't take a random sample because there is only one possible transition so you would take the transition remembered in model table.